Manufacture of artificial stone



COMPUSI i was, tAAlVHNti-l COATING OR PLASTiC i7 Patented May 13, 19412,241,604

t l /Q7 UNITED STATES PATENT OFFICE MANUFACTURE OF ARTIFICIAL STONENorman Victor Sydney Knibbs, New Barn, Longfield, and Alfred PetterPehrson, Streatham, London, England, assignors to The ContinentalInvestment Syndicate Limited, London, England No Drawing.ApplicationFebruary4, 1936, Serial ,Q/

1503.5 62,298. In Great Britain February 12, 5-

21 Claims. (Cl. 25-155) This invention relates to moulded building byvirtue of the fact that the sulphate very rapblocks, artificial stone,paving slabs, moulded idly goes into solution and the lime then hydratespipes and posts, and like products which are proin a solution of calciumsulphate. duced by a process which consists in mixing It is necessary toavoid the use of a mixture ground lime and a silice s and o :4 -,i 5 toorich in quicklime or of too rapidly slaking material, which may becalcined, with water lime, otherwise the heat generated through hymou mgor otherwise forming the mixture to dration raises the temperature inthe mixture shape, and hardening by the action of steam at above theboiling point of the aqueous solution, pressures above atmospheric; italso re a es to in which case the lime may hydrate in the orirt'ic'le's'si'ibh asb dilding blocks which are made dinary way, with expansion, andthe block will porous by the addition of aluminium dust or by bedisintegrated or weakened. It may be indicatother known means before aremng. ed that at least 5% og t hemixture is quicklime.

Hitherto it has generally been thought advisand for all ordinarypurpdse's with'solid (i. e. nonable to avoid the use of cellular orsc-called non-porous) articles the permentiticus materials, bu here havebeen procentage would be from 10% up to about mhydrated lime and makingwhile on the other hand, where fluid mixtures provision for expansionwhile the material was containing large proportions of waterare used,setting in the moulds, in which case the moulds for example in makingcellular or so -called porwere specially constructed to withstandpressure. ous blocks and like articles, the percentage of We havediscovered that it is possible to use 20 quicklime need never be lessthan 10 and may unhydrated lime in such moulded or otherwise goconsiderably higher than the limit above statiormed products without thenecessity for forced. In mixtures as immediately above indicated iblyrestraining the material against expansion in the temperature would notnormally go beyond the moulds while it issetting,,and, moreover, thatthat of the boiling point of the mixture, but in the inclusion ofunhydrated lime has certain imcases where a mixture very rich in lime isdeportant advantages. sired, the temperature may be kept down byAccording to the present invention, a cementiusing partially hydratedlime or a mixture of tious product is derived by causing the admixtureuicklime and Hydrated lime instead of pure of a siliceous and/orargillaceous material and uickli'me. "'I'Ee lime should preferably not eguick lime with a compound of an oxz-acid of wwiland should [Te-of arelatively s F ur adding water, mould n or 0 er Se rapid sla mg n 1nd,otherwise the blocks have to s p mg the mixture to the required form,allowbe 'kept for a long time between moulding and ing the lime in themixture to hydrate and hardsteaming, with consequent disadvantages.ening by the action of s te am under pressure, The vWe have found thatthe rate of hydration of moulded or otherwise formed article is firstleft the lime can conveniently be controlledtdso'me for a periodsuflicient to allow hydration of sub- Extent 'byvariation of thetemperature pi the stantially all the lime in the mixture and then'water' psed in mixinmhigher the tiiip'era-' hardened by treatment withsteam under presture dfizli'Efititbf'iised in the mixture is thequicksure, er the mixture sets, but if the initial temperature Whenthere is added to the mixture calcium 40 of the water is too high, themixture loses fluidity sulphate (or other salt of a Fxz-acid ofsulfififiri, before it passes out of the mixture, and it is or w en forthe si ceous an /or argi aceous matherefore convenient to use water at atemperaterials are selected ones which are rich in oxyture of Q -;35Should the lime in the mixture acid of sulphur compounds, or rich incompounds be very active, or should there be a high perwhich, throughthe subsequent treatment they centage of quicklime, the initialtemperature receive in the process, will produce an oxy-acid should beless than that above stated. of sulphur compound, we have found thatpro- In making solid, 1. e. non-porous, blocks withvided there issuflicient water present to ensure out artificially produced porosity,one method of hydration taking place in the presence of liquid, carryingout the process may be outlined as folthe lime hydrates withoutexpansion or with only lows: The lime is ground to a fineness of aboutvery slight expansion, and provided hydration of the lime issubstantially complete before steamhardening, there is no expansionduring the hardening process. It is thought that the action of per centpassing a sieve of meshes to the linear inch, and is mixed with thesiliceous or argillaceous material for example san in a' pro c may be 7parts of sand 53 1 part ,gflgipmsglphate con re s y a 1on 0 9 Brigg 0fllme, and 3 per cent of grouncwws added.

Water is added and mixed with the solids, the amount, which may be fromto 40 per cent, or within wider limits, being dependent on the nature ofthe material used and the proportion of lime. The mixture is madesufliciently wet to be suitable for moulding. The wet mixture istransferred to moulds, which may, if desired, be vibrated during orafter filling, and the moulds are set aside for a period sufficient forthe hydration of the lime, which period may be one or two hours, or maybe overnight, by which time the block will have become sufficiently setfor it to be withdrawn from the mould, it being sufllciently hard forall ordinary handling, and much harder than an unsteamed sand-limebrick. Before withdrawal from the mould, or at any time between fillingand withdrivval'ffhe material may be levelled off flush with the top ofthe mould, using a suitable knife or other device. The blocks are thentransferred to an autoclave and subjected to the action ofsaturated"'steam .unde 1; pressure, for example for E hours'at l fiblbs. per square inch gauge pressure.

There are several advantages in the process described over that usingfully hydrated lime.

Hitherto the only satisfactory process has been that employed in makingsand-J1me. bricks, in which process the mixture of sand and hydratedlime is mixed with just suflicie'i'itfigtefto'm'efk Tt'cohere whencompressed, and the mixture moulded under high pressure to the form ofbricks. Owing to the high'fno'ulding pressure required to givesufflcient strength to permit handling in the unsteamed state and togive suflicient strength and density in the final product, the processis not economically applicable to large blocks. If more water is addedso that the mixture can be moulded without pressure, in the same manneras, for example, concrete blocks are made, the final result isunsatisfactory because there is shrinkage and surface cracking or otherdefects develop during steaming. Moreover the blocks must be left in themoulds until steamed because they are too soft to handle. Furthermore,the steamed blocks are not as strong as" sand-lime bricks made in theusual manner.

Blocks made according to the present invention do not shrink. During thehydration of the lime there'appears to be a very slight expansion sothat a sharp moulding is produced. The moulded block may be removed fromthe mould before steaming, thus economisin in moulds and saving space inthe autoclave. The blocks after hydration of the lime but beforesteaming are firm but not hard and are in a condition well adapted toscraping of the surface. or other treatment to produce a finish of adesired kind. The amount of we; required to produce a block suitable formoulding without pressure is less than when hydrated lime is employed.and a portion of this water is taken up by the lime in hydration, sothat the water content of the block to be steamed is much less than itwould be if hydrated lime were used in the mixture. In consequence, amuch denser block may be produced and one of much higher strength.Unlike in the sand-lime brick process, large blocks may be made asreadily as small ones.

In making oious blo c ks. one method of carrying out the css maybeoutlined as follows:

China cla is calcined at a temperature 800 tolfifi 0f, 0., mixed withguicklime and ypsum P'-k.... .VAW-

and the mixture iround together to a of about '75 percen passing sieveof 200 meshes eness '77 per cent calcined cla 20 per cent lime and 3 percent gypsum. To the ground mum is "porositFGFtfie block may becontroll'd'ii'ot only by the amount of aluminium or other agent added,but also by the amount and Jempgraturq of water used in mixing; forexample 'we have 'Tlf'n d'ihat with the admixed water at a temperatureof 40 C. instead of 15 C., the porosity is doubled W1 powderedaluminium. After standing an hour or more the slurry will have set to aplastic or semi-plastic mass and before steaming the tops of the blocksmay be struck oil? level and the blocks divided up by cutting, asmentioned below. They are then hardened by the action of steam underpressure as in the case of solid b oc s. s n' e pre ous example, thelime hydrates during standing and the mass sets, but it is not as hardas the solid blocks and ordinarily it is left in the moulds during thesteaming process.

The use of quicklime has important advantages over the use of hydratedlime in making porous blocks. Ordinarily, the hydration of the limeproceeds simultaneously with gas production and the heat of hydrationpromotes the latter. By choosing correctly the quantity of water used inmixing, and also its temperature, the block will set (lose its fluidity)when, or soon after, gas production is complete, and this prevents lossof gas by coalesence of the bubbles to form large ones which rise to thesurface. Such loss it is difllcult to avoid when hydrated lime is used.These porous blocks may also be cut to size by means of knives afterthey have set but before steam-hardening, and in this way there is aneconomy in cost of production. As with solid blocks, the strength ofporous blocks made from quicklime is higher than those made fromhydrated lime.

We have found that it is possible to use a large number of differentsiliceous and argillaceous substances in our process and that thesesubstances may be used either in the raw state or after calcination. Ingeneral, siliceous substances, such as sands, granite sands andchippings, and the mite. are not improved by calcination, whilst claysand shales yield relatively poor results if they Have not been calcined.We have found that the exact temperature of calcination of clay or shaledoes not directly influence the so strength of the blocks made to anygreat extent.

but a high temperature of calcination generally results in a lowerquantity of water being required in mixing, which favours high strength.Furthermore, we have found that a rather high 55 temperature ofcalcination generally results in to the linear inch. The proportionsused may be blocks of high quality by our process. Colliery where itrises like leav engd dough, owing to the bUlVH'Uoi l lune,

shale, moreover, ordinarily contains suiiicient sulphur, in the form ofpyrites or otherwise, to produce in burning with limestone forefi'ecting the necessary conversion of calcium carbonate to quicklime,sufficient calciu m su lphate for the process to render the addition ofmore gypsmn unnecessary. Low value oil shales or oil shale residues, andother bitumales', may mthe same way. e es ra e emperature of calcinationis about 900-1000 C. The resulting calcined mixture finely ground and isthen ready for mixing with ater and, for porous blocks, with aluminium.

It will be appreciated that although in the foregoing description themoulded articles referred to have been indicated as building blocks, theinvention is not limited in this way; for example, it may be equallyapplicable to paving slabs, etcetera, and extends to all other articlessuch as pipes, posts, decorative mouldings, and in fact to most articleswhich ordinarily might be expected to be cast or moulded from concrete,plaster of Paris, and like products, or from articles formed from thosematerials upon a core or in a former of metal or other material. It isapplicable to pipes and other articles moulded by centrifugal force asin the "Hurne process of making concrete pipes.

The invention further contemplates the addition to the mixture ofaggregates, such for example as gravel, granite chippings. etcetera, andmore especially it contemplates the addition of an asbestos aggregate toproduce solid or porous ar es 0 an asbestos cement nature.

What we claim is:

1. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, shaping to the required form, andapplying steam under pressure to harden.

2. A method of making a precast artificial stone product that comprisesmixing quicklime with at least one of the materials defined as siliceousand argillaceous and containing or admixed with a compound of anoxy-acid of sulphur, adding water to hydrate the quicklime, shaping tothe required form, and applying steam underpressure to harden.

3. A method of making a precast artificial stone product that comprisesgrinding, mixing and calcining calcium carbonate and at least one of thematerials defined as siliceous and argillaceous and containing oradmixed with a compound of an oxy-acid of sulphur, adding water tohydrate the quicklime produced in the calcination of the calciumcarbonate, shaping to the 'required form, and applying steam underpressure to harden.

4. A method of making a precast artificial stone product that comprisesmixing quicklime with at least one of the materials defined as siliceousand argillaceous and at least one of which materials contains or isadmixed with a substance that when calcined with the quicklime yields acompound of any oxy-acid of sul-' phur, adding water to hydrate thequicklime,

of hydrated lime and at least 5 percent quicklime, adding water tohydrate the quicklime, shaping to the required form, and applying steamunder pressure to harden.

6. A method of making a precast artificial stone product that comprisesmixing with quick lime at least one of the materials defined assiliceous and argillaceous and at least one of which materials containsor is admixed with a substance that when calcined yields a compound ofan oxy-acid of sulphur, adding water to hydrate the quicklime, shapingto the required form, and applying steam under pressure to harden.

7. A method of making a. precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, shaping to the required form,rendering the mass porous, and applying steam under pressure to harden.

8. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, shaping to the required form,adding a gas-generating agent to the mass to render it porous, andapplying steam under pressure to harden.

9. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, shaping to the required form,adding powdered aluminum to the mass to render it porous, and applyingsteam under pressure to harden.

10. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, placing the mass in a formingmeans, removing the hydrated mass from the forming means after it hasbecome hardened sufilciently to permit handling, and applying steamunder pressure to harden the mass further.

11. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, shaping to the required form,varying the temperature of the added water to control the rate ofhydration of the quicklime, and applying steam under pressure to harden.

12. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a compound of an oxy-acid of sulphur,adding water to hydrate the quicklime, shaping to the required form,adding a gas-generating agent to the mass to render it porous, varyingthe temperature of the added water to control the gas generation,

I an oxy-acid of sulphur and an aggregate, adding water to hydrate thequicklime, shaping to the required form, and applying steam underpressure to harden.

14. A method of making a precast artificial stone product that comprisesmixing with approximately three per cent gypsum at least one of thematerials defined as siliceous and argillaceous and at least five percent of which is quicklime in the proportion of approximately sevenparts of the said material or materials to one part of the lime, addingwater to hydrate the quicklime, shaping to the required form, andapplying steam under pressure to harden.

15. A method of making a precast artificial stone product that comprisesmixing approximately 77 percent calcined clay, 20 percent quicklime and3 percent gypsum, adding water to hydrate the quicklime, shaping to therequired form, and applying steam under pressure to harden.

16. A method of making a precast artificial stone product that comprisesmixing approximately 77 percent calcined clay, 20 percent quicklime, 3percent gypsum and a small amount of a gas-generating agent, addingwater to hydrate the quicklime, shaping to the required form, andapplying steam under pressure to harden.

17. A method of making a precast artificial stone product that comprisesmixing approximately 77 percent calcined clay, 20 percent quicklime, 3.percent gypsum and 0.1 percent aluminum, adding water to hydrate thequicklime, shaping to the required form, and applying steam underpressure to harden.

18. A method of making a precast artificial stone product that comprisesmixing sulphurcontaining shale with calcium carbonate, calcining theshale and the calcium carbonate, thereby effecting inburning of thesulphur with the calcium carbonate to produce quicklime and an oxy-acidof sulphur compound, grinding the calcined mixture, adding water tohydrate the quicklime, shaping to the required form, and applying steamunder pressure to harden.

19. A method of making a precast artificial stone product that comprisesmixing sulphurcontaining shale with calcium carbonate, calcining theshale and the calcium carbonate, thereby efiecting inburning of thesulphur with the calcium carbonate to produce quicklime and an oxy-acidof sulphur compound, grinding the calcined mixture, adding agas-generating agent, adding water to hydrate the quicklime, shaping tothe required form, and applying steam under pressure to harden.

20. A method of making a precast artificial stone product that comprisesmixing at least one of the materials defined as siliceous andargillaceous with quicklime and a small percentage of alime-hydrating-controlling compound of an oxy-acid of sulphur, addingwater to hydrate the quicklime, shaping to the required form, andapplying steam under pressure to harden.

21. A method of making a precast artificial stone product that comprisesmixing quicklime with at least one of the materials defined as siliceousand argillaceous and at least one of which materials contains or isadmixed with a metallic sulphide that when calcined with the quicklimeyields a compound of an oxy-acid of sulphur, adding water to hydrate thequicklime, shaping to the required form, and applying steam underpressure to harden.

NORMAN VICTOR SYDNEY KNIBBS. ALFRED PETTER PEI-IRSON.

